362 Chapter 12
Figure 12.2 The appearance of skeletal muscle fibers through the light microscope. The striations are produced by
alternating dark A bands and light I bands. (Note the peripheral location of the nuclei.)
Nuclei
Muscle fiber
Somatic motor neuron axon
Muscle fiber nucleus
Nerve fiber branches
Mitochondria
Folded sarcolemma
Synaptic vesicles
Neuromuscular cleft
Motor end plate
Motor end plate
Myofibril
(a)
Neuromuscular junction
Somatic motor axons
Motor end plate of muscle fiber
Muscle fibers
(b)
Figure 12.3 Motor end plates
at the neuromuscular junction. The
neuromuscular junction is the synapse
between the nerve fiber and muscle fiber.
The motor end plate is the specialized
portion of the sarcolemma of a muscle fiber
surrounding the terminal end of the axon.
( a ) An illustration of the neuromuscular
junction. Notice the slight gap between the
membrane of the axon and that of the muscle
fiber. ( b ) A photomicrograph of muscle fibers
and neuromuscular junctions.